It is nice to be polite on the boards and I subscribe to that more than most but arrant nonsense has to be challenged. Your note ignores dates and confuses rule with genetics. It is simply not true that everyone in the isles is Norse/Viking. It is true that the the western isles were firmly under Norse rule from about 800 to just after 1100 ad. Even when the rulers changed, the descendants of Somerled were part Norse. However, there is no suggestion that the earlier population disappeared and that is why they were known as the Gall/Gael, a mix of Gaels and 'strangers.' Afetr c. 1100, the topping up of the population was overwhelmingly from mainland Scotland and not from anywhere remotely Norse. Accordingly, the latest DNA studies show a mix including a significant minority with a marker Norse gene.
As to this particular line of postings, there are at least six entirely separate origins of the MacPherson i.e. son of the parson, lines that I can name. Only one of them, the descendants of Rory or Roderick, half brother of John Muidertach MacDonald the great 8th Captain of Clnaranald, might well have been of Norse origin. His descendants show up in Ardnamurchan and Moidart. If any found their way to the western isles, they are few and far between and will have been concentrated in the Clanranald territories of Benbecula and South Uist and not in the otherwise 'more Norse' islands to the North. The MacPhersons in those latter islands are probably mostly descendants of the 'Red Parson' an O'Docherty mercenray soldier priest who led the gallowglass element of the forces of Uisdean MacDonald when he took over part of Skye and established Clan Donald North in about 1369. Those MacPhersons settled in Trotternish in Skye and as the Liosadair or linen workers, later spread southwards to North Uist and Benbecula. Absolutely nothing Norse about their origins though they may of couse over he centuries have picked up some [much diluted] Norse blood through marriage.
I hope this helps but please do avoid unsupportable ex cathedra statements that can only serve to mislead the unwary.